Google can do a lot of things, but a new study says it can’t estimate flu activity across the United States with a high degree of accuracy. A University of Washington study says Google Flu Trends is about 25% less accurate at estimating flu rates in the U.S. than the Center for Disease Control’s (CDC) national flu monitoring programs.
Dr. David Ortiz, who led the university study, says search activity isn’t necessarily the best way to gauge the flu’s spread.
“Internet search behavior is likely different during anomalous seasons such as during 2003-4,” explained Dr. Ortiz. “We hypothesize that during periods of intense media interest or unexpected influenza activity such as the 2009 H1N1 influenza pandemic, Google Flu Trends may be least accurate at estimating influenza activity.”
Google launched Flu Trends in late 2008. In its announcement, Google said that certain search queries are more common during flu season, “and we found that there’s a very close relationship between the frequency of these search queries and the number of people who are experiencing flu-like symptoms each week.” Google even suggested its flu trends tool is more valuable than the CDC’s data:
The CDC does a great job of surveying real doctors and patients to accurately track the flu, so why bother with estimates from aggregated search queries? It turns out that traditional flu surveillance systems take 1-2 weeks to collect and release surveillance data, but Google search queries can be automatically counted very quickly. By making our flu estimates available each day, Google Flu Trends may provide an early-warning system for outbreaks of influenza.
The study says the problem isn’t Google’s technology; it’s that flu-like illnesses are “actually caused by the influenza virus in only 20 percent to 70 percent of cases during the influenza season.” In other words, a lot of us think we have the flu and search Google accordingly … but quite often we don’t really have the flu.
Ultimately, the study says Google Flu Trends is a Good Thing, but the data should be taken with the proverbial grain of salt:
“Google Flu Trends influenza surveillance provides an excellent public health service, because it provides nationwide influenza activity data in a cheap and timely manner,” said Dr. Ortiz. “Nevertheless, our study demonstrates that its data should be interpreted with caution and that other surveillance systems more accurately reflect influenza activity in the United States.”
(hat tip: ResourceShelf)